Molding products of chlorinated vinyl chloride-based resins have a feature of high heat resistance and are used in application uses relatively at high temperature, for which existent molding products of vinyl chloride-based resins can not be used because of heat deformation. For example, by utilizing that their heat deformation temperature is higher by 20 to 40° C. than that of the vinyl chloride resin molding products, their use includes pipes for hot water and joints thereof, or sheets for use in home electronics undergoing heat.
On the other hand, it has been known that the molding products of the vinyl chloride-based resin are poor in the impact resistance. Since the impact resistance is poor, when pipes made of chlorinated vinyl chloride-based resins are cut by a pipe cutter, pipes can not be cut neatly to sometimes cause chipping or cracking. Further, such drawbacks sometime result in cracking by machining or the like also in joints, sheets or plates, so that it has been demanded for molding products of chlorinated vinyl chloride-based resins with improved impact resistance. For improving the impact resistance, it is known by Canadian Patent No. 722769 to blend an ABS resin with a chlorinated vinyl chloride-based resin composition and it is known by U.S. Pat. No. 3,646,163 to blend an MBS resin in a chlorinated vinyl chloride-based resin composition. However, while the blends provide an effect of improving the impact resistance, they involve a problem of moldability such as burning due to its high melt viscosity upon molding. Further, in a case of injection molding joints or the like with the blend described above, it also results in a problem of blooming on the surface, resulting in a problem that no molding product having good surface property can be obtained.
On the other hand, for lowering the melt viscosity during molding thereby improving the moldability, JP-B-49-18102 proposes blending an ABS resin and/or MBS resin with chlorinated polyethylene in a chlorinated vinyl chloride-based resin composition. Further, U.S. Pat. No. 5,194,471 proposes blending of an ABS resin having a predetermined Shore D hardness and a chlorinated polyethylene in a chlorinated vinyl chloride-based resin composition with an aim of improving the drop weight impact strength at a low temperature of a pipe as described in ASTM D 2846. In the chlorinated vinyl chloride-based resin compositions, while moldability such as burning is improved and the effect of improving the impact resistance is also observed, the problems of blooming on the surface of the molding products can not be solved in a case of applying the blends described above to the injection molding of joints, etc., and it has been demanded for a chlorinated vinyl chloride-based resin composition capable of obtaining favorable surface property in the injection molding of joints, etc. while maintaining heat resistance, impact strength and moldability.
Further, in a case of large-sized injection molding products where the weight of the molding product is as large as about 3 kg or more such as a joint of 10 inch φ diameter, since the impact strength can be kept to some extent by the effect of wall thickness, importance is attached particularly to the heat resistance, the moldability and the surface property rather than the impact strength. In such large size injection molding, abnormality for the surface property tends to occur due to heat generation under sharing in the nozzle during injection molding and excellent moldability is an essential condition because of large size of the molding products. However, known compositions are poor in the moldability and involve a serious problem for the surface property of accompanying worsening of the surface property (blooming) and it has been demanded for a chlorinated vinyl chloride-based composition of excellent heat resistance, moldability and surface property.